Enphase Backup Storage - DIY Self-Installer Hurdles

[summit]

Of course, but when there is low solar irradiation and no grid power, you need some other form of backup. And a generator with a 48VDC output has the highest overall efficiency to charge the backup battery.

if you have an EV, that's another option to charge the 48vdc pack. It should be on rare occasion

 

[DER Solar]

Most EV's don't have the V2L inverter, Tesla EV's don't have it, and on newer EV's it is an option only available on the higher end trims. There is also a 3.6KW limit. There are some workarounds available EV Extend.

 

[DER Solar]

Part #2: IQ8+ AC Coupled to XW Pro 6848:
Schneider XW Pro 6848: Firmware 2.04.00bn29
IQ Gateway: Software 7.3.120
IQ8+: (4 total) Firmware 521-00005-r05-v02.48.01
Grid Profile: IEEE 1547-2015 (Colorado default)
PV Amp Meter (CT): PZEM-022 AC Current Voltage Amperage Power Energy Panel (AC Volt, AC Amp, Frequency (Hz), PF)

Off-Grid Test:
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the micro-grid
4 x IQ8+'s produce about 1.2 kW = 4 x 299W
SOC 100%: XW Pro raises frequency by 1 Hz to 61 Hz, IQ8+'s shut off within 1-2 seconds.
XW Pro frequency back to 60 Hz, IQ8+'s stay off
SOC drops to about 99%: IQ8+ inverters lock-on again after 5 min and 20 sec.
works with or without IQ gateway connected

On-Grid ... Grid-Fault/Off-Grid ... On-Grid Test:
Grid Voltage: 249V
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the grid
about 1.2 kW PV flows into the grid and into the batteries
On Grid-Fault: IQ gateway reboots, micro-inverters switch off
Inverter Voltage: 240V, about 9v less than grid, IQ8's log change in voltage
After about 4.5 minutes, the IQ8's lock on to the micro-grid and produce 1.2 kW
Grid-Back: IQ8's switch off, lock on after 4.5 sec and produce 1.2 kW

 

[wheisenburg]

Part #2: IQ8+ AC Coupled to XW Pro 6848:
Schneider XW Pro 6848: Firmware 2.04.00bn29
IQ Gateway: Software 7.3.120
IQ8+: (4 total) Firmware 521-00005-r05-v02.48.01
Grid Profile: IEEE 1547-2015 (Colorado default)
PV Amp Meter (CT): PZEM-022 AC Current Voltage Amperage Power Energy Panel (AC Volt, AC Amp, Frequency (Hz), PF)

Off-Grid Test:
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the micro-grid
4 x IQ8+'s produce about 1.2 kW = 4 x 299W
SOC 100%: XW Pro raises frequency by 1 Hz to 61 Hz, IQ8+'s shut off within 1-2 seconds.
XW Pro frequency back to 60 Hz, IQ8+'s stay off
SOC drops to about 99%: IQ8+ inverters lock-on again after 5 min and 20 sec.
works with or without IQ gateway connected

On-Grid ... Grid-Fault/Off-Grid ... On-Grid Test:
Grid Voltage: 249V
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the grid
about 1.2 kW PV flows into the grid and into the batteries
On Grid-Fault: IQ gateway reboots, micro-inverters switch off
Inverter Voltage: 240V, about 9v less than grid, IQ8's log change in voltage
After about 4.5 minutes, the IQ8's lock on to the micro-grid and produce 1.2 kW
Grid-Back: IQ8's switch off, lock on after 4.5 sec and produce 1.2 kW

I would say that is a fairly successful test. So far, it is doing nothing unexpected and performing better than I was expecting.

I am still concerned about pumping 8000-9000 watts into the inverter if I ever have a power failure in full sun and the batteries are fully charged. I have some ideas on how to rewire my system to allow the following:

1. Grid power is on (use 240 Volts AC from AC1 Grid In). The PV contactor should always be energized. Relays controlling each individual string would also always be on. Excess production will flow back to the grid.

2. Grid power is off (use 240 Volts AC from AC1 Grid In). The PV contactor will only be energized when SOC or battery drops below a certain point. This should be possible by setting up the Auxiliary relay control signal.

3. Grid power is off (use 240 Volts AC from AC1 Grid In). Only turn on selected PV strings. This might need some level of management. It might be different between winter and summer.

4. Power the Envoy board from the AC Load Out (so it does not reboot every time the PV contactor disconnects).

There is still a potential issue if the inverter disconnects for a reason other than a full power failure or during the time when power has come back on, but the inverter has not yet reconnected to the grid. It appears the Schneider can still knock the PV inverters off line if it needs to. I have noticed that after a grid failure, the PV inverters do not just suddenly come back on at 100%. They ramp up slowly which should give the Schneider time to do its "Frequency Pulse" thing. I have also seen this same frequency pulse when I have been testing with the battery above the SOC where you would expect the Schneider to dump its excess power into the battery.

So from what I am seeing, a couple things are true.

1. If your system SOC is above the level where AC coupled charging should occur: You need to have enough Inverter and Battery Capacity to handle the excess output of the PV inverters and store it in the batteries long enough for the Schneider to send its "Pulse of Death" to the PV inverters to get them to shut down. Without a PV disconnect mechanism, I believe this will happen over and over every 5 minutes.

2. If your system SOC is below the level where AC coupled charging should occur: You need to have enough Inverter and Battery Capacity to handle the excess output of the PV inverters and store it in the batteries long enough for the Schneider to ramp down the the PV inverters (through frequency shifting) to a level that is in line with usage and battery charging requirements.

In other words, when AC coupling you want to maximize the amount of battery and inverter power, while also minimizing the amount of PV (or at least getting it down to a manageable level).

For me at least (knock on word) I am hoping that true grid down situations will be fairly rare and will not be extended. Maybe further testing will show that the Schneider can manage all of this out of the box without any additional addons. We shall see.

FYI, before I fine tuned my charging parameters, I had the charging set to 140 amps per inverter. I think this is the default. So with two inverters and three batteries, I was pumping 14,000 watts into the batteries. They can handle up to 100 amps each, so this was an acceptable load. Anyway when the chargers turned on, I was sure my system was about ready to "Blow". There was an enormously loud 60 cycle hum. It turns out it was just wire tray covers resonating and nothing was actually wrong. Just because your system can handle a load doesn't mean you really want to put that much load on it. It seems far happier charging at 30 amps per inverter / 20 amps per battery.

 

[solar8484]

Part #2: IQ8+ AC Coupled to XW Pro 6848:
Schneider XW Pro 6848: Firmware 2.04.00bn29
IQ Gateway: Software 7.3.120
IQ8+: (4 total) Firmware 521-00005-r05-v02.48.01
Grid Profile: IEEE 1547-2015 (Colorado default)
PV Amp Meter (CT): PZEM-022 AC Current Voltage Amperage Power Energy Panel (AC Volt, AC Amp, Frequency (Hz), PF)

Off-Grid Test:
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the micro-grid
4 x IQ8+'s produce about 1.2 kW = 4 x 299W
SOC 100%: XW Pro raises frequency by 1 Hz to 61 Hz, IQ8+'s shut off within 1-2 seconds.
XW Pro frequency back to 60 Hz, IQ8+'s stay off
SOC drops to about 99%: IQ8+ inverters lock-on again after 5 min and 20 sec.
works with or without IQ gateway connected

On-Grid ... Grid-Fault/Off-Grid ... On-Grid Test:
Grid Voltage: 249V
4 x IQ8+'s take about 5 min 15 sec for the micro-inverters to lock on to the grid
about 1.2 kW PV flows into the grid and into the batteries
On Grid-Fault: IQ gateway reboots, micro-inverters switch off
Inverter Voltage: 240V, about 9v less than grid, IQ8's log change in voltage
After about 4.5 minutes, the IQ8's lock on to the micro-grid and produce 1.2 kW
Grid-Back: IQ8's switch off, lock on after 4.5 sec and produce 1.2 kW

Good progress. If 18+ iQ8+ can sustain AC coupling with a XW PRO at full output then I would consider it a pretty solid confirmation of compatibility.

 

[summit]

Most EV's don't have the V2L inverter, Tesla EV's don't have it, and on newer EV's it is an option only available on the higher end trims. There is also a 3.6KW limit. There are some workarounds available EV Extend.

true, but it sure beats turning on the noisy smelly generator, for those, hopefully, rare occasions. It's so annoying that my next door neighbor who has the Ioniq i6 with a 3kw 120vac outlet, is still operating his ridiculous noisy generator to 2am.

 

[DER Solar]

More Details on IQ8 AC Coupling:
XW Pro FW power curtailment is pretty fast! 60Hz to 6o.2 Hz and IQ8's cut power in half, at 60.4 Hz they shut off, all within 2-3 seconds!
IQ8's wait 5 minutes then lock back on and FW cycle starts again with no battery hysteresis.

One key difference between IQ gateways:
2019 800-00555-r03 (IQ Gateway) full PLC signal strength, reboots during grid-fault,
2021 800-00655-r09 (IQ Gateway) reports reduced PLC signal strength!, stays on during grid fault,
has redesigned switched power supply, same PLC ASIC as IQ7's and IQ8's

IQ Gateway is not required for AC coupling!

More Testing To Do:
- Adjust XW Pro AC backup AC voltage to match grid voltage and check if IQ8's detect grid-fault
- Test AC coupling of Hoymiles HMS-2000 micro-inverter with full 2 kW, 4 x 500W PV input, using UL1741 SB CA Rule 21 profile
(Hoymiles has excellent documentation how UL 1741 SA controls are implemented)
- add PLC filter to see if IQ gateway (800-00655-r09) reports better signal strength
- One final problem to be solved, imho: How to handle or limit the max possible PV inrush current on a grid-fault not exceeding the XW Pro battery charge max current.

 

[DER Solar]

Hoymiles HMS-2000 (4 x 500W) AC Coupling:
Grid- Profile: UL1741 SB CA Rule 21 profile

On-Grid:
After 5 minutes, HMS-2000 locks onto grid and starts producing, full 2000W after 6 minutes total.

Grid-Fault:
HMS-2000 switches off, stays off for about 7 minutes, then locks onto micro-grid and ramps up production to 2000W for one more minute.

SOC FULL:
As SOC approaches 100%, XW-Pro FW kicks in and ramps up frequency from 60 Hz to 62 Hz, reducing HMS power production linearly down to 0 at 62 Hz, takes several seconds.,

SOC below 100%:
After about 4 minutes, HMS-2000 resumes power production up to 2000W.
FW cycling works fine depending on SOC.

Grid-BackOn:
HMS-2000 stays connected and feeds excess power into battery first, then into grid.

Overall Impression:
The HMS-2000 does not heat up at all during 2000W production, much less than 4 x IQ8+ at 1200W.
Has very low stand-by consumption, about 50mW for the 2000W unit.
Hoymiles inverters are well engineered and will be able to challenge the grip Enphase has on micro-inverters especially the dual and quad modules.
I'm ordering 6 x HMS-700 UL 1741 SB inverters to replace a 12 IQ8+ subarray to see how well they'll perform.

 

[zanydroid]

znydroid: you can get 48V DC generators for charging batteries directly, has best overall efficiency for battery charging. EG4 has a new 48V 100A charger you could connect to a 240V generator, but it does not have any CAN Bus or ModBus controls. And at night, as you've suggested, you'll better off with using the generator on the AC side. May be you should get 2 generators?

Thanks, missed this previously. Since I am space constrained I don’t want too many generators sitting around.

The Chargeverter can probably be set to a generally safe fixed charge setting and then hard disconnected with a contactor as needed to integrate with automation.

One open question is how much I’m willing to manually manage the system when grid is down, and how long the system needs to work in my absence without intervention. I believe the gold standard is to have the inverter auto start and auto exercise stationary generators.

 

[zanydroid]

SOC FULL:
As SOC approaches 100%, XW-Pro FW kicks in and ramps up frequency from 60 Hz to 62 Hz, reducing HMS power production linearly down to 0 at 62 Hz, takes several seconds.,

Does the XW Pro have published limits on ratio or amount of AC coupled solar vs battery or DC coupled solar?

 

[kennyb]

Hoymiles HMS-2000 (4 x 500W) AC Coupling:
Grid- Profile: UL1741 SB CA Rule 21 profile

On-Grid:
After 5 minutes, HMS-2000 locks onto grid and starts producing, full 2000W after 6 minutes total.

Grid-Fault:
HMS-2000 switches off, stays off for about 7 minutes, then locks onto micro-grid and ramps up production to 2000W for one more minute.

SOC FULL:
As SOC approaches 100%, XW-Pro FW kicks in and ramps up frequency from 60 Hz to 62 Hz, reducing HMS power production linearly down to 0 at 62 Hz, takes several seconds.,

SOC below 100%:
After about 4 minutes, HMS-2000 resumes power production up to 2000W.
FW cycling works fine depending on SOC.

Grid-BackOn:
HMS-2000 stays connected and feeds excess power into battery first, then into grid.

Overall Impression:
The HMS-2000 does not heat up at all during 2000W production, much less than 4 x IQ8+ at 1200W.
Has very low stand-by consumption, about 50mW for the 2000W unit.
Hoymiles inverters are well engineered and will be able to challenge the grip Enphase has on micro-inverters especially the dual and quad modules.
I'm ordering 6 x HMS-700 UL 1741 SB inverters to replace a 12 IQ8+ subarray to see how well they'll perform.

Amazing. Thank you for this information. I've been eyeing the Hoymiles, but haven't read much on them operating in a microgrid generated by an xw.

 

[kennyb]

Does the XW Pro have published limits on ratio or amount of AC coupled solar vs battery or DC coupled solar?

This is what the Schneider Ac couple guide says

" *125% of maximum allowable charge power of the battery (calculated as rated
continuous charge current times rated charge voltage).

*125% of continuous rating of XW Pro inverter(s).

For example, if battery inverter is rated for 6.8 kW of continuous power at 40°C and
battery pack is rated for 3.75 kW at 40°C, then the PV inverter must be no more than
125% of lesser of two which is 4.68 kW at 40°C."

Beyond that I haven't ever seen a hard limit published

 

[zanydroid]

This is what the Schneider Ac couple guide says

" *125% of maximum allowable charge power of the battery (calculated as rated
continuous charge current times rated charge voltage).

*125% of continuous rating of XW Pro inverter(s).

For example, if battery inverter is rated for 6.8 kW of continuous power at 40°C and
battery pack is rated for 3.75 kW at 40°C, then the PV inverter must be no more than
125% of lesser of two which is 4.68 kW at 40°C."

Beyond that I haven't ever seen a hard limit published

Ok, the battery side of this is a little easier to understand than for victron (which is also a lot more restrictive).

I’m also thinking about an XW Pro with HM series microinverter (probably not HMS).

I was considering whether using the HM DTU’s export limit feature to dynamically stay below the limit for whatever inverter I AC couple the HM micros with. My house is somewhat “overpaneled” in that I have a lot of micros and panels, but not that many of them will ever turn on at once.

 

[DER Solar]

Let's look at it from a different angle:
XW Pro is rated at 6.8 kW. One battery pack could be 2 kWh but could sink 200A, or another battery pack could be 20 kWh but sink only 50A. Let's assume for now, that the battery pack is sized above the XW Pro max charge rating of 140A, a typical battery XWPro can handle 200A or more.

125% of 6.8 kW is about 8.5 kW. So the AC coupling guide would allow you to size the PV array up to 8.5 kW. This is ok with the usual losses, soiling, high panel temps in summer. But what about a clear cold winter day with -25 deg F, panels very clean and panels producing more that their standard rating? 8.5 kW at 250V is about 34 Amp. No significant home loads and all PV energy flows into the grid.
Then we'll have a grid fault: The PV AC 34 Amp needs a sink to go! That's about 5 x 34A = 170A DC charging, the XW Pro can handle only 140A max DC charge current so it will fault immediately, or worse, it may get damaged! So the 125% rule of thumb works most of the time until it doesn't!

So what would be a safe PV upper limit regarding the XW Pro 140A max charge current?
PV = 5 kW: AC max = 20A max DC charge current: 100A
PV = 6 kW: AC max = 24A max DC charge current: 120A
PV = 7 kW: AC max = 28A max DC charge current: 140A

All of these calculations assume that the XW Pro can dump the max charge current into the battery on a grid-fault.
Depending of SOC, the XW Pro charge current limit on a grid-fault may be a lot less.

 

[DER Solar]

zanydroid:
Maybe the Victron battery rules are more realistic to guarantee a sink for the PV inrush current on a grid-fault.
HM inverters are fine, I need the HMS with 900 Mhz because I have a metal roof. The export limit will work, but it needs to be fast enough to curtail the inrush current. If allowed, you want to export the max possible, but when a grid fault happens you want to limit production immediately to the max inrush current allowable, not sure it can be done that fast, about 20 ms.

 

[zanydroid]

Yes, that limit needs to be calculated relative to the minimum of kW AC or kW DC on the solar side. With kW AC being simpler and probably the more likely constraint to be hit assuming overpaneling.

I was looking at XW Pro manual last night and it didn’t call out a smaller limit for when the charging is limited by CV. Presumably the AC coupling would have to be shut down around CV. Or surge back to CC temporarily while waiting for the solar to cut back.

The Hoymiles export limiter will automatically adjust AC output limit, however it is a dynamic control protocol coordinated across multiple sources, with some response lag and RF losses. I believe ncsolarelectric has measured 30 second response time. My thinking is it would need to be set to enforce a lower limit than XW Pro (or other system) design guideline to compensate for all this handwaviness

 

[zanydroid]

Maybe the Victron battery rules are more realistic to guarantee a sink for the PV inrush current on a grid-fault

Victron has a one size fits all recommendation for all their inverters (ie independent of charge current), of 1.5 kW-AC per 5 kWh of Lithium batteries.

I think XW limit pushes a lot more responsibility to the installer, since they expect you to sort out what the maximum safe charge current for your battery is.

If allowed, you want to export the max possible, but when a grid fault happens you want to limit production immediately to the max inrush current allowable, not sure it can be done that fast, about 20 ms.

Yes, I haven’t written down the whole control flow but this was part of what I had in my head. I think you would want this grid down behavior as well as a few others. Having a PLC drive a safety relay to cut off the inverters would be a good idea. Especially in combination with something that can cut the current when above the limit.

I believe HM inverters will respond to RF with only PV power active, not AC power. I can see inverters not properly connected to AC on my monitoring. If this is the case then you can reprogram it with the AC cut.

For a PLC system the transmitter would have to work even if AC is cut

 

[Hedges]

Then we'll have a grid fault: The PV AC 34 Amp needs a sink to go! That's about 5 x 34A = 170A DC charging, the XW Pro can handle only 140A max DC charge current so it will fault immediately, or worse, it may get damaged! So the 125% rule of thumb works most of the time until it doesn't!

...

All of these calculations assume that the XW Pro can dump the max charge current into the battery on a grid-fault.
Depending of SOC, the XW Pro charge current limit on a grid-fault may be a lot less.

If AC coupled battery inverter can't stuff all the power that comes in, Line voltage will shoot up (inductor delivering current), and I think GT PV inverter disconnects. If no one made any attempt to do anything with the current, high voltage spike could kill something. Inductors have a reputation for that, and any driver needs to protect itself.

This may require intelligent programming of the battery inverter, to clip overshoots so voltage is limited yet cause immediate GT PV disconnect. It might have to absorb the energy of one switch-mode step, or one half-cycle of AC. Absent the next phase, GT PV won't output anything (shutting off AC waveform would be extreme, but might work - or not depending on what degenerate resonant "island" the loads present.

Any AC powered device has to survive kV spikes (voltage but limited time and energy.) I would expect battery inverter to clamp voltage overshoots. These may be some of the trade secrets or patents in the industry.

 

[wheisenburg]

Of course, but when there is low solar irradiation and no grid power, you need some other form of backup. And a generator with a 48VDC output has the highest overall efficiency to charge the backup battery, and you do not even need an inverter generator for this.

At least in my situation, I have fairly reliable power. If I can get AC coupling to work as a back up, for most of the year I have excess solar power. It is really only Dec, Jan where usage is significantly greater than production. So if I look at my actual "Solar Deficit" it is only a few hundred KW a year in those months. So how many outages will I have in those months and how long will they last?. Generator electricity when you factor in gas, plus the generator cost (their life time is maybe 1000 to 2000 hours) is probably close to $2.50 a KWH. So if I needed a 20 KWH boost for three days during a year, that's $150.00 a year. If I can gain 20% efficiency, I save $30.00 a year. So is it worth buying 2 generators to improve the efficiency? I am thinking to go with a small generator and an separate EG4 charger.

Run a small (and quite) inverter 3000-4000 watt generator into a EG4 charger that accept 120 as well as 240 and it can provide a daily battery top off during those dark months. The generators in this size range all seem to be 120 volts which the EG4 does accept. Unless you are truly off grid and will be running on generators a significate amount of time, capital cost is going to be more important than efficiency. If you plug a generator directly into a hybrid inverter it will need to power all your AC loads, plus have enough left over to charge the battery. So you will need 10000 to 13000 watt 240 volt generator. Much more $$$.

As an added benefit a small quite generator can be used for other purposes like camping, tailgating and jobsites.

 

[zanydroid]

overall I agree with the analysis on efficiency vs capital cost.

If you plug a generator directly into a hybrid inverter it will need to power all your AC loads, plus have enough left over to charge the battery.

It depends on if hybrid is generator assist, whether it needs full capacity. Also if you plug directly in you need the voltage to be compatible with what the inverter wants, usually 120/240 inverter needs 240 generator, which then pulls in need for a bigger generator or a transformer on a 120v generator. Not bad but costs more than a chargeverter.

And you also lose the ability to modulate the AC coupled solar, which is probably the killer during the day.

So charger into the battery and taking the efficiency hit.

One issue I see with coupling through the chargeverter is that I doubt whether that specific charger is UL listed and can be permitted for installation. I’m also unclear on whether supplemental chargers need to be covered by UL9540 listing of the ESS. I want to say that this makes logical sense given that one can easily hide the battery with a misconfig.